Contact speed control in springdriven step type switches



June 1, 1954 T. c. LENNOX 2,680,164

CONTACT SPEED CONTROL IN SPRING-DRIVEN STEP TYPE SWITCHES Filed March19, 1952 it 42 4a Inventor: Thom as O. Lenncx,

y u A HIS flute? figy June 1, 1954 T. c. LENNOX 2,680,164 CONTACT SPEEDCONTROL IN SPRING-DRIVEN STEP TYPE SWITCHES Filed March 19, 1952 2Sheets-Sheet 2 Inventor; Thomas OL'ennox,

Hus fittorney.

Patented June 1, 1954 CONTACT SPEED CONTROL IN SPRING- DRIVEN STEP TYPESWITCHES Thomas C. Lennox, Pittsfield, Mass, assignor to GeneralElectric Company, a corporation of Application March 19, 1952,

6 Claims.

This invention relates to spring-driven electrical switching mechanismsand more particularly to contact speed control nisms of the step type.

Step type switching mechanisms are widely used in connection with stepvoltage regulators in which a voltage is adjusted by stepping a contactmember from one voltage tap to another.

classes. The first of these classes is the type in which the stepcontacts are moved by a spring drive, with the spring itself beingenergized by a motor drive. The second broad class is that in which thestep contacts are actuated by a direct motor drive.

The speed with which the movable contacts of a step type switchingmechanism are moved with respect to the stationary contacts of themechanism is an important factor with respect to the the contact speedobtainable using direct highspeed direct motor drives for step typecontacts requires a starting, stopping, and positioning "system for themotor which is expensive and frequently a source of trouble.

Accordingly, it is an object of my invention to increasing the lifeexpectancy of step type electrical contacts of the spring-driven type.

It is a further object of my invention to provide a new and improveddevice for obtaining optimum contact speed with spring-driven step typeelectrical contacts.

In accordance with these objectives, my invention provides incombination with spring driven step-type contacts means for modifyingthe motion of the movable contacts with respect to the stationarycontacts in such manner as to .obtain optimum relative speed of thestationary Serial No. 277,351

2 and movable contacts from the standpoint of life expectancy of thecontacts.

The features of this invention which I believe to be novel are set forthwith particularity in the appended claims. My invention itself, however,both as to its organization and use, together with further objects andadvantages thereof, may best be understood by referenc to the followingdescription taken in connection with the accompanying drawing in whichFig. l is a perspective view of a step type voltage regulator apparatusincorporating one embodiment of the contact speed control arrangement ofmy invention in accordance with which a paddlewheel speed control deviceis used; Fig. 2 is a view of a modified type of speed control devicewhich is connected view of a modified embodiment of my invention inwhich the speed control is obtained by use of a piston acting in adashpot member.

Referring now to the drawing, there is shown therein a pair of powerlines I and 2 which may be connected either to the source or load sideof an electrical system. Power line i is connected to one end of a shuntwinding 3 of a step type voltage regulator in a well known manner. Powerline 2 is connected to the mid-tap of a switching reactor 1, throughwhich it is connected to the series winding 4 of the voltage regulator,as will be explained more fully herein- The line I is connected to lineI at the point where line I is connected to shunt winding If lines l and2 are connected to the electrical source, then lines circles describedby conducting rings 8 and 9, and by the conducting segments 6.

In order to maintain electrical contact beto the view shown in thedrawing, with a pair of contact brushes H and ii which are conductivelyconnected together. Contact H maintains contact with radially innerconducting ring 8 while contact 12 maintains contact with the conductingsegments 3 which are connected to the taps 5 of the series winding l.Thus, the upper end of the switching reactor 1 is connected throughradially inner conducting ring 8, and contacts ll and I2 to theconducting segments 8 and thence to the taps of series winding 4.

In order to provide electrical contact between the lower end of theswitching reactor E, with respect to the view shown in the drawing, andthe contact segments 6, the left-hand edge of the contact arm H) isprovided with a pair or con tact members l3 and id which areconductively connected together and respectively maintain contact withradially outer conducting ring 3 and the contact segments 6. Thus, thelower end of the switching reactor 1, is connected through conductingring 9 and contacts l3 and i i to conducting segments 6 which are inturn connected to the respective taps oi the series winding i. Thecontacts H and i2 carried by contact arm it are insulated from contactsi3 and Hi.

When the position of the contact arm it is such that contact arm If) andcontacts Ii, i2, i3 and M are in contact with only a single one of theconducting segments 6 then the respective contacts ll, l2, l3 and M areall at the same electrical potential since they are short circuited bythe particular conducting segment s with which the contact arm i0 is inalignment. In this case, the current divides between the two halves ofthe switching reactor I, the two halves on the winding being in parallelelectrical relation with each other. However, if the position on thecontact arm i0 is such that it bridges a pair of adjacent conductingsegments 6, as shown in the view in the drawing, then each end of theswitching reactor 1 is connected across a different tap of the serieswinding 4. When this occurs, the switching reactor acts as anautotransformer and the voltage derived is half way between the voltagesof the adjacent taps to which the respective opposite ends of switchingreactor 1 are connected.

The switching arm i0 is driven by a shaft 15 which is actuated by aspring-driven Geneva gear mechanism which will now be described.

A motor it drives a pinion l? which engages a gear l8. Gear H3 is fixedto a shaft H3 at the opposite end of which is positioned a pinion ill.Pinion 26 engages a gear 2! which is loosely mounted on and rotatesfreely about shaft 22. A pin 23 is integrally attached to gear 2| androtates therewith. A lug member 24 is integrally attached to shaft 22and is in the path of rotation of pin 23. A crank 25 is rigidly attachedto one end of shaft 22. The radially outer portion of crank 25 ispivotally attached to a pair of spiral spring members 26 and 21 whichare each respectively fastened at their opposite ends to fixed pivotpoints.

When gear 2| is caused to rotate, pin 23 engages lug 24 and causes therotation of shaft 212. Rotation of shaft 22 causes an elongation ofspring members 26 and 2'5. When crank mem ber 25 moves slightly past thedead center position, which is about 180 displaced from the posi tion ofcrank 25 as shown in the drawing, the action of springs 26 and 21 causesthe crank 25 and shaft 22 to move rapidly back to the position shown inthe drawing thereby discharging the energy stored in the springs duringthe period in which they were being elongated. At the other end of shaft22 segment 28 having projecting ears i9 is rigidly mounted on and turnswith shaft 22. A Geneva gear driver 36 is loosely mounted on shaft 22and is in engagement with Geneva gear 32 mounted on shai't it. Duringthe portion of the cycle of rotation of shaft 22 when shaft 22 and crank25 are being moved back from overcenter position by the springs 26 and.21, the segment 28 engages the Geneva gear driver 3B in drivingrelation and causes pin member iii of the Geneva gear driver 30 to dropinto the slot between a pair of adjacent teeth of Geneva gear 32 tothereby advance the Geneva gear 32 by one tooth pitch with a rapidmotion. Motion of Geneva gear 32 actuates shaft it] so as to movecontact arm it from one conducting segment 6 to another.

As mentioned hereinbefore, it has been found that the speed with whichthe contact arm I0 is moved by the action of the spring drive mechanismjust described is such that the life of contacts carried by contact armit, such as contacts H, l2, l3 and i l, and also the life of thestationary conducting segments 6, is sometimes reduced considerablybelow the life expectancy which could be obtained if the contact speedwere not so high as that produced by the rapid action of the overcentersprings ".25 and 2'? which drive the Geneva gearing mechanism.

One theory which explains the reduced contact life with the contactspeeds normally produced by spring driven mechanisms is describedhereinafter. It will be understood, of course, that while this theoryprovides a theoretical explanation of the improved performance obtainedin accordance with my invention, that there may also be otherexplanations of the changes in contact liie characteristics observed dueto the operation of my invention.

The erosion of the moving and stationary contacts is known to be relatedto the value of the current, to the voltage which appears across theopen contacts, to the duration of the arc and to the resistance of theare. There may also be some increase in the erosion due to bouncing ofthe contacts when closing.

The first two items just mentioned are determined by the design of theregulator windings and circuit, but the other three, namely, duration ofthe arc, resistance of the arc, and bouncing oi the contacts, may bevaried by varying the contact speed in opening or closing. When contactscarrying alternating current are opened under oil or other insulatingliquid, the current usually stops at a current nerd-that is, at a pointwhen the alternating current wave is passing through zero. lhe result isthat if the actual interruption occurs at the first current zerofollowing the physical opening of the contacts, little more can be doneto shorten the duration of the arc. On the other hand, the resistance ofthe arc is afiected by the length of the are so that if the contactspeed is made very high so as to draw the are out to considerable lengthduring the period before the first current zero the resistance may beunnecessarily increased. As an increase in resistance will result inincrease of energy dissipated in the arc and possibly an increasedburning of the contacts, such increased arc resistance should beavoided.

Considering these factors, I have determined that there can be anoptimum condition where serted between the paddle wheel and the speed ofthe opening of the contacts is sufficient to cause a currentinterruption at the first current zero but yet not high enough to undulylengthen the are physically during the interval between the mechanicalopening of the contacts and the point at which the first current zero isreached. In other words, too low a contact opensistance before the firstcurrent zero is reached. The optimum s eed consequently is between thesetwo extremes.

In accordance with my invention, I provide a means for controlling thespeed of the moving contacts, and particularly the speed with which thecontacts are opened, by use of an energy absorbing device which will nowbe described.

In the embodiment of my invention shown in Fig. 1, I provide an impeller33 of the paddle wheel type which is driven by shaft l through theengagement of gear 34 which is rigidly attached to the outer end ofshaft l5 and pinion 35 which is mounted on the same shaft with impeller33. The relative diameters of gear 34 on shaft l5 and pinion 35 are suchthat the angular velocity of pinion 35 is substantially greater thanthat of a shaft [5. The impeller 33, as well as all of the otheroperating elements shown in Fig. l, is immersed in oil or some otherinsulating liquid. Hence, a considerable amount of energy is required tocause the rotation of the paddle wheel in the liquid. Thus, a large partof the energy of the springs 26 and 27 is absorbed by the impeller 33and, as a result, the speed of rotation of the shaft is reduced belowwhat the speed would be if an energy absorbing device were not used.

When the springs 26 and 2! discharge, moving the shaft i5 through therequired angle, the speed of the shaft 1 5 instead of rising to amaximum which is limited only by the inertia of the parts and incidentalfriction, as would be the case without the use of the energy absorbingdevice of my invention, will instead rise only to such speed absorbingsubstantially the whole torque imparted to the system by the springs.

The best or optimum speed of opening of the contacts may be determinedby tests on specific cases, and then a mechanism designed to move thecontacts at the required speed. In applying an impeller or paddle wheelto a spring-driven switch for the purpose of obtaining the requiredspeed, a favorable factor is that the torque resulting from the movementof such an impeller in the insulating liquid varies approximately as thesquare of the speed, thus making it much easier to obtain a desiredspeed than would be the case if the torque-speed relation were purelylinear. Having determined the relation of the torque to speed for agiven size of the impeller or paddle wheel, appropriate gearing may beinthe spring drive such that substantially the full torque imparted bythe springs will be balanced by the reverse torque of the paddle wheelat the required speed. If, then, due allowance is made for the frictionand inertia of the switch contacts, the design is fixed.

- The reduction in speed obtained using the impeller device inaccordance with my invention has the further advantage that it reducesthe tendency of the contacts to bounce when closing.

This tendency to bounce decreases rapidly as the speed of the contactsis decreased and, consequently, a decrease in speed to obtain theoptimum speed condition at opening reduces the tendency of the movingcontact to bounce when closing. The burning of the contacts due tobouncing is primarily due to the drawing of short arcs while thecontacts are open during the bouncing. Each such are burns or erodes thecontacts to some degree. In experiments which I have made I have foundthat in contact systems suitable for step-voltage regulators bouncing ofthe contacts on closing is substantially completely eliminated when thespeed of the contacts is such as to provide the optimum opening speed ashereinbefore described.

A further feature of my invention as shown in the embodiment of Fig. 2is the provision of an impeller or paddle wheel device havin a iiy wheelor inertia characteristic to aid in the closing of the contacts. It isknown that satisfactory action of a spring driven switch for astep-voltage regulator usually involves inertia forces. That is, theclosing of the contacts occurs without any tendency to stop at theposition where the contacts first engage because of the inertia of therapidly moving parts. When, however, the speed of the contacts issubstantially reduced in order to obtain optimum arcing conditions, thisinertia effect is substantially reduced, and may be less than requiredfor satisfactory closing of the contacts. The energy stored in themoving contact system varies as the square of the speed of the contactmotion. Thus, if the speed is reduced to one-third, for example, thestored energy is reduced to one-ninth. In order to avoid diiiiculty ofthis nature, the inertia forces may be restored by addingweight to therim of the impeller or paddle wheel which is geared so as to operate athigher speeds than the contacts themselves.

There is shown in Fig. 2 my preferred arrangement for providing optimumspeed for opening spring-driven electrical contacts and, at the sametime, providing sufficient inertia to the contact closing system toinsure that the contact as will result in the impeller 33 properlycloses without sticking. In the embodiment of Fig. 2 I have provided aflywheel effect for the impeller or paddle wheel by addingciroumferentially distributed weight to the radially outer portion ofthe impeller. In the particular structure shown in Fig. 2, I haveprovided the impeller 48 with a disk member 49 having most of its weightconcentrated in its radially outer or rim portion. However, it will beunderstood that the flywheel effect may be obtained in other ways suchas, for example, concentrating weight in the radially outer portions ofthe paddle members 36 of the impeller 33 of Fig. l. The amount of weightthat must be added to the impeller rim to restore the necessary inertiaforces which pre- Thus, if the rim of disk 69 moves five times as fastas the contacts themselves, only as much weight need be added to theimpeller rim as to the contacts to store the same energy.

In the arrangement of Fig. 2, which is the preferred embodiment of myinvention, the impeller is connected into the gearing system in asomewhat different manner than is shown in Fig. 1. In the arrangement ofFig. 2, shaft 29 is driven by a motor in the same manner as shown inFig. 1 and pinion 20 is attached to shaft 59 and drives gear M which isloosely mounted on shaft 22. Pin 23 is attached to gear 2! and rotatestherewith. When pin 23 engages lug 24 which is rigidly attached to shaft22, shaft 22 is caused to rotate and tensions spring 26 due to therotation of crank 25 at the end of shaft 22. The arrangement thus fardescribed is the same as that of Fig. 1. In accordance with the modifiedarrangement, the impeller 48 is directly driven by the shaft 22 throughthe gears 51 and 52 rather than being driven by the shaft Hi to whichthe Geneva gear 32 is attached, as in the arrangement of Fig. 1. Gear 5!is rigidly attached to shaft 22 and rotates therewith. Gear 5| drivespinion 52, which is rigidly mounted on the same shaft as impeller 48causing the rotation of impeller l8. With this arrangement, the powerimparted by the spring 28 to the shaft 22 divides and the major portionis transmitted directly through gears 5i and 52 to the impeller 48 andonly that part of the power which is needed to operate switch arm I istransmitted through the Geneva gearing mechanism. Thus, the wear on theGeneva gear is reduced as com pared to the arrangement of Fig. 1.Moreover, as the impeller 48 is always connected through gears and 52 toshaft 22 no undue acceleration of shaft 22 occurs and hence there is nodanger that Geneva driving pin 3! will enter the slot of Geneva gear 32at excessive speed.

With the arrangement shown in Fig. 2 it will be observed that theimpeller 48 is put into motion during the winding or extending of thespring by the motor. However, this occurs at relatively low speed andhence does not place any appreciable additional load on the motor.

There is shown in Fig. 3 a modified embodi-- ment of my invention inaccordance with which a piston and dash-pot arrangement is substitutedin place of the paddle wheel impeller 33 of Fig. 1 and serves the samefunction as the paddle wheel.

As seen in Fig. 3, a piston rod 31 is pivotally attached at one end tocrank member which is in turn 'igidly attached to shaft 22. The pistonrod 31 is attached at its other end to a piston 38 which moves in acylinder 39 in such manner as to expel oil or some other liquid from asuitable orifice 10 in the cylinder 39. The cylinder 39 is immersed inan insulating liquid and the liquid is drawn into the cylinder throughorifice t9 on the upstroke of the piston, and expelled through orificeso on the downstroke of the piston. Thus, the motion of the piston inthe cylinder provides a dashpot action whic absorbs some of the energytransmitted from the springs 26 and 21 to the shaft i5 in a mannersimilar to that previously described in connection with impeller 28.

A further feature of the construction shown in Fig. l and which may alsobe used with the embodiment of Fig. 2 is an arrangement for re versingthe polarity connections of the series winding 3 when the switch arm l0passes through its neutral position. A reversing switch 4% is providedin series with line 2. Reversing switch i! is movable into engagementwith either contact 12 or 43, these respective contacts being connectedto opposite ends of the series winding i. A pin member A l is attachedto Geneva gear 32 at a position such that as Geneva gear 32 passesthrough the neutral position corresponding to the position at whichswitch 41 should be moved from contact :32 to contact 43 or vice versa,the pin 44 engages the slot in Geneva segment 8 l5 and causes arapid'rnotion of reversing shaft 46 which is connected to Geneva segment45 through link 41. Shaft :26 is connected to switch ll in such mannerthat motion of shaft 46 causes switch member ti to move from contact 62to contact at or vice versa.

From the foregoing, it can be seen that I have provided in accordancewith invention a new and improved arrangement for controlling the speedof step type contacts of the spring-driven type by providing anarrangement for absorbing a part of the energy supplied to thespring-driven contacts. In providing such an energy absorbing device forspeed control of the contacts, I have substantially increased the lifeexpectancy of such contacts, and studies which I have made indicate thatthe life expectancy of contacts whose speed is controlled in accordancewith my invention is increased as much as 500% over the life expectancyof the prior art springdriven step type contacts.

While there have been shown and described particular embodiments of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications can be made therein without departing from theinvention and, therefore, it is aimed in the appended claims to coverall such chan es modifications as {all within the true spirit and scopeof the invention.

What I claim as new and desire to secure by Letters Patent or the UnitedStates is:

1. In an electrical switching mechanism of the step type in which amovable electrical contact is moved with a rapid motion out ofengagement with a first fixed electrical contact and into engagementwith a second electrical contact, a spring driven operating means formoving said movable electrical contact, said operating means comprisingan overcenter spring, and an energy absorbing device operativelyconnected to said operating means to retard the speed with which saidmovable contact moves out of engagement with said first fixed contact,said energy absorbing device comprising a paddle wheel rotatable in aliquid, said paddle wheel having a substantial portion of its masscircumferentially distributed about its radially outer periphery toprovide a iiywheel effect to prevent sticking between said movablecontact and said second fixed contact upon initial engagement of saidmovable contact and said second fixed contact.

2. A sprlng-actuated electrical switching device comprising, incombination, a motor, afirst shait, a crank member, said crank memberbeing rigidly mounted on said first shaft, a spring, one end of saidspring being pivotally connected to the radially outer end of saidcrank, said spring being tensioned by rotation of said crank, saidspring moving said first shaft with a rapid motion when said spring ismoved to an overcenter position by rotation of said crank, a secondshaft, gear means connecting said first shaft in driving relation tosaid second shaft, an electrical contact carried by said second shaft, afixed electrical contact engageable with said contact carried by saidsecond shaft, engagement of said contacts normally completing anelectrical circuit, second shaft being driven by said first shaft todisengage said contacts when said first shaft is moved by said spring,and an energy absorbing means mounted for rotation in a liquid anddirectly driven by said first shaft to decrease the speed of rotation ofsaid first shaft when said first shaft is driven by said spring.

3. In an electrical switching mechanism of the p type in which a movableelectrical contact is moved with a rapid motion out of engagement with afixed electrical contact, a spring driven operating means for movingsaid movable elec" trical contact, said operating means comprising anovercenter spring, and an energy absorbing device operatively connectedto said operating means to decrease the speed with which said movablecontact moves out of engagement with said fixed contact, said energyabsorbing device comprising a piston movable in a liquid-containingdashpot.

4. An electrical switching device of the step type comprising aplurality of spaced apart fixed electrical contact members lying on thecircum-- ference of a circle, an arm mounted for rotation about an axiswhich passes through the center of said circle upon which said contactmembers lie, said arm carrying a contact member engageable with at leastone of said fixed contact members in substantially all positions of saidarm, said arm being rotatable in both a clockwise and a counterclockwisedirection, means for rotating said arm comprising a motor, a shaftdriven by said motor, a crank member attached to said shaft, a springmember pivotally connected to a radially outer portion of said crankmember, said spring member being tensionedby rotation of said crank,said shaft being operatively connected to said contact-carrying arm,rotation of said spring member past overcenter position causing saidspring member to discharge and move said shaft with a rapid motion, thecontact carried by said arm being moved out of engagement with a firstfixed contact and into engagement with a second fixed contact duringsaid rapid motion of said shaft, and an energy absorbing device drivenby said shaft to reduce the speed with which said contact carried bysaid rotatable arm moves out of engagement with said first fixedcontact.

5. An electrical switching device of the step type comprising aplurality of spaced apart fixed electrical contact members lying on thecircumference of a circle, an arm mounted for rotation about an axisWhich passes through the center of said circle upon which said contactmembers lie, said arm carrying a contact member engageable with at leastone of said fixed contact members in substantially all positions of saidarm, said arm being rotatable in both a clockwise and a counterclockwisedirection, means for rotating said arm comprising a motor, a shaftdriven by said motor, a crank member attached to said shaft, a springmember pivotally connected to a radially outer portion of said crankmember, said spring member being tensioned by rotation of said crank,said shaft being operatively connected to said contact-carrying arm,rotation of said spring member past overcenter position causing saidspring member to discharge and move said shaft with a rapid motion, thecontact carried by said arm being moved out of engagement with a firstfixed contact and into engagement with a second fixed contact duringsaid rapid motion of said shaft, and a liquid-immersed energy absorbingdevice rotatably driven by said shaft to reduce the speed with whichsaid contact carried by said rotatable arm moves out of engagement withsaid fixed contact.

6. An electrical switching device of the step type comprising aplurality of spaced apart fixed electrical contact members lying on thecircumference of a circle, an arm mounted for rotation about an axiswhich passes through the center of said circle upon which said contactmembers lie, said arm carrying a contact member engageable with at leastone of said fixed contact members in substantially all positions of saidarm, said arm being rotatable in both a clockwise and a counterclockwisedirection, means for rotating said arm comprising a motor, a shaftdriven by said motor, a crank member attached to said shaft, a springmember pivotally connected to a radially outer portion of said crankmember, said spring member being tensioned by rotation of said crank,said shaft being operatively connected to said contact-carrying arm,rotation of said spring member past overcenter position causing saidspring member to discharge and move said shaft with a rapid motion, thecontact carried by said arm being moved out of engagement with a firstfixed contact and into engagement with a second fixed contact duringsaid rapid motion of said shaft, and a liquid-immersed energy absorbingdevice rotatably driven by said shaft to reduce the speed with whichsaid contact carried by said rotatable arm moves out of engagement withsaid first fixed contact, said energy absorbing device comprising apaddle wheel, said paddle wheel having a substantial portion of its masscircumferentially distributed about its radially outer periphery toprovide a flywheel effect to prevent sticking between said movablecontact and said second fixed contact upon initial engagement of saidmovable contact and said second fixed contact.

References Cited in the file of this patent UNITED STATES PATENTS

